Your brain gets sent back in time 10 years. You wake up in your younger body but with all your memories from the past decade.

Damn, I would change everything. I'd start by going aggressively vegan at the age of 9, just to make a point. I'd be more hostile towards people who didn't respect me and my beliefs, make fewer frienemies, and call out flagrant abuse as it occured. I'd run away from home a couple of times when life got tough, ace every test ever with minimal studying, and get a job at the pool I work at sooner. I would do more work around the house because my mom was always way too fucking loaded down and I was super lazy.

Oh, and I would invest in Bitcoin. There are probably better investments to make, but I would have to know them offhand for them to benefit me.